Imprint lithography template comprising alignment marks

ABSTRACT

A system of determining and correcting alignment during imprint lithography process is described. During an imprint lithographic process the template may be aligned with the substrate by the use of alignment marks disposed on both the template and substrate. The alignment may be determined and corrected for before the layer is processed.

CROSS-REFERENCE TO RELATED APPLICATIONS

[0001] The present application is a divisional of U.S. patentapplication Ser. No. 09/907,512 filed on Jul. 16, 2001 entitled “HighResolution Overlay Alignment Methods and Systems for ImprintLithography,” which claims priority to U.S. Provisional PatentApplication No. 60/218,568 filed on Jul. 16, 2000 entitled“High-Resolution Overlay Alignment Methods and Systems for ImprintLithography,” both of which are incorporated by reference herein.

STATEMENT REGARDING FEDERALLY SPONSORED RESEARCH OR DEVELOPMENT

[0002] The U.S. Government has a paid-up license in this invention andthe right in limited circumstances to require the patent owner tolicense others on reasonable terms as provided for by the terms ofN66001-98-18914 awarded by the Defense Advanced Research Projects Agency(DARPA).

BACKGROUND OF THE INVENTION

[0003] The present invention relates to methods and systems to achievehigh-resolution overlay alignment for imprint lithography processes.

[0004] Imprint lithography is a technique that is capable of printingfeatures that are smaller than 50 nm in size on a substrate. Imprintlithography may have the potential to replace photolithography as thechoice for semiconductor manufacturing in the sub-100 nm regime. Severalimprint lithography processes have been introduced during 1990s.However, most of them have limitations that preclude them from use as apractical substitute for photolithography. The limitations of theseprior techniques include, for example, high temperature variations, theneed for high pressures and the usage of flexible templates.

[0005] Recently, imprint lithography processes may be used to transferhigh resolution patterns from a quartz template onto substrate surfacesat room temperature and with the use of low pressures. In the Step andFlash Imprint Lithography (SFIL) process, a rigid quartz template isbrought into indirect contact with the substrate surface in the presenceof light curable liquid material. The liquid material is cured by theapplication of light and the pattern of the template is imprinted intothe cured liquid.

[0006] Using a rigid and transparent template makes it possible toimplement high resolution overlay as part of the SFIL process. Also theuse of a low viscosity liquid material that can be processed by lightcuring at low pressures and room temperatures lead to minimalundesirable layer distortions. Such distortions can make overlayalignment very difficult to implement.

[0007] Overlay alignment schemes typically include measurement ofalignment errors between a template and the substrate, followed bycompensation of these errors to achieve accurate alignment. Themeasurement techniques that are used in proximity lithography, x-raylithography, and photolithography (such as laser interferometry,capacitance sensing, automated image processing of overlay marks on themask and substrate, etc) may be adapted for the imprint lithographyprocess with appropriate modifications. The compensation techniques haveto be developed keeping in mind the specific aspects of imprintlithography processes.

[0008] Overlay errors that typically need to be compensated for includeplacement errors, theta error and magnification error. Overlaymeasurement techniques have been significantly improved during recentyears as the minimum line width of photolithography processes havecontinued to shrink. However, these techniques may not be directlyapplicable to the imprint lithography processes.

SUMMARY OF THE INVENTION

[0009] The embodiments described herein include methods and systems thatare applicable for overlay alignment scheme in imprint lithographyprocesses.

[0010] In general a method of forming a pattern on a substrate may beaccomplished by applying a light curable liquid to a substrate. Thelight curable liquid may include any liquid curable by the applicationof light. Typically light curable compositions are compositions that mayundergo a chemical change in the presence of light. Light that mayinduce a chemical change includes ultraviolet light (e.g., light havinga wavelength between about 300 nm to about 400 nm), actinic light,visible light, infrared light and radiation sources such as electronbeam and x-ray sources. Chemical changes may be manifested in a numberof forms. A chemical change may include, but is not limited to, anychemical reaction that causes a polymerization to take place. In someembodiments the chemical change causes the formation of an initiatorspecies within the lens forming composition, the initiator species beingcapable of initiating a chemical polymerization reaction.

[0011] In an embodiment, the light curable composition may be aphotoresist composition. Photoresist compositions include anycomposition that is curable by exposure to UV light. A characteristic ofphotoresist compositions is that only the portion of the compositionthat is exposed to light (e.g., ultraviolet light) may undergo achemical reaction. Any of a variety of photoresist materials commonlyused in the semiconductor industry may be used. In one embodiment, thelight curable composition includes an acylate monomer.

[0012] In most photolithographic processes, photoresist materialstypically have a high viscosity (greater than about 20 centipoises(cps). In imprint lithography, the use of high viscosity liquids maymake it more difficult to produce sub 100 nm structures. It has beenfound that low viscosity liquids produce much more accurate reproductionof sub 100 nm structures. In one embodiment, the light curable liquidmay have a viscosity below about 20 cps, preferably below about 10 cps,and more preferably below about 5 cps.

[0013] After the light curable liquid is applied to the substrate, thepatterned template is oriented above the portion of the substrate towhich the light curable liquid was applied. In the semiconductorprocessing, a plurality of semiconductor devices may be formed on asingle substrate. Each individual semiconductor device may be formed ofa plurality of layers. These layers may be sequentially formed with eachlayer overlying the previously formed layer. Because of the smallfeature size of the individual components of semiconductor devices, thealignment of each layer with respect to the other layers may be crucialto the proper functioning of the semiconductor device. A method andsystem for aligning a patterned template with a predetermined locationon a substrate is herein described.

[0014] In one embodiment, the patterned template may include a templatealignment mark. The substrate may include a substrate alignment mark.After the patterned template is positioned over the substrate, thealignment of the template alignment mark with respect to the substratealignment mark is determined. If the template alignment mark does notalign with the substrate alignment mark the orientation of the patternedtemplate with respect to the substrate may be altered until the marksare substantially aligned. Moving the substrate with respect to thetemplate may compensate errors in which the template alignment mark andthe substrate alignment mark are offset in the X-Y direction. This maybe accomplished by a substrate support stage configured to allowcontrolled movement of the substrate in the X-Y direction. Theta errorsmay be corrected by altering the angle of the template with respect tothe substrate. Magnification errors may be corrected by altering thephysical dimensions of the template.

[0015] A variety of alignment marks may be formed in either the templateand/or the substrate. In some embodiments, the alignment mark may beformed by etching a portion of the template with a predeterminedpattern. Alternatively, a thin film of a second material may be formedon the template. The second material may be deposited in a pattern thatis complementary to the substrate alignment mark. The second materialmay be opaque to light, however, the pattern of the template alignmentmark may be reproduced in the cured liquid on the substrate.Alternatively, the second material may be substantially transparent tothe wavelengths of light that are used to cure the light curable liquid.The second material, however, may have different optical properties atnon-curing wavelengths of light. When analyzed using an analyzer at thenon-curing wavelengths of light, the alignment mark may be readilydetected. During curing, however, the alignment mark is substantiallytransparent to the curing light and the liquid under the alignment markmay be substantially cured. In one embodiment, the deposited secondmaterial is Si₂O₃. In another embodiment, the template alignment markmay be produced by etching of the template. The template alignment markmay be formed from a series of parallel lines that together act as adiffraction grating. The diffraction grating template alignment mark maybe readily observable when determining the alignment of the templatealignment mark with respect to the substrate alignment mark. Duringcuring, however, the diffraction grating template alignment mark may besubstantially transparent to the curing light, due to the relative largespacing of the etched lines with respect to the wavelengths of lightused for curing.

[0016] A variety of sensing methods may be used to determine thealignment of the template alignment mark and the substrate alignmentmark. In one embodiment, images of the alignment marks on the templateand substrate are focused on the same imaging plane. This focusing maybe accomplished by the use of illumination sources with two distinctwavelengths and an image processing technique to separate focused imagesfrom out-of-focus images. Alternatively, images of the alignment markson the template and substrate may be focused on the same imaging planeby using two distinct illumination sources with polarization andpolarizing arrays above the template surface. In another alternative,Moiré pattern-based alignment error measurement techniques may be used.During Moiré patterned-based alignment the gap where the measurement istaken may be made as small as it possible without template-substratecontact in order to minimize focusing problems of the two layers of theMoiré patterns. A high resolution (sub 100 nm) measurement and activecontrol of gap over the entire template-substrate interface may be used.Any of these sensing methods may be used in conjunction with any of theabove-described alignment marks.

[0017] In some embodiments, the gap between the patterned template andthe substrate may be substantially filled prior to determining thealignment of the template and the substrate alignment marks. In otherembodiments, the substrate and/or the patterned template alignment marksmay be difficult to visualize when the gap between the patternedtemplate and the substrate is substantially filled with liquid. Inanother embodiment, the liquid may be disposed on the substrate in apredetermined pattern. When the template is brought into contact withthe liquid, only a portion of the template may be in contact with thetemplate. By controlling the pattern of liquid applied to the substrateand the location of the alignment mark on the substrate, the templatemay be positioned in contact with the liquid such that a portion of thetemplate that includes the alignment mark is not in contact with aliquid. In this manner the template alignment mark may be aligned withthe substrate alignment mark without the interference of the liquid.After the template alignment mark is aligned with the substratealignment mark the patterned template may be positioned with respect tothe substrate such that the gap between the patterned template and thesubstrate is substantially filled.

[0018] Alternatively, when the template is brought into contact with theliquid, only a portion of the template may be in contact with thetemplate. By controlling the pattern of liquid applied to the substrateand the location of the alignment mark on the substrate, the templatemay be positioned in contact with the liquid such that a portion of thetemplate that includes the alignment mark is not in contact with aliquid. In this manner the template alignment mark may be aligned withthe substrate alignment mark without the interference of the liquid.After initial contact of the template with the liquid, the pattern ofliquid will spread out beneath the template until the liquidsubstantially fills the gap between the template and the substrate.Alignment of the template alignment mark and the substrate alignmentmark may be accomplished as the gap is filing up with liquid.

[0019] In some embodiments, the template may need to be corrected formagnification errors induced on the substrate from processing of theprevious layer. Magnification errors may occur when a template orphotolithographic mask used to process a previous layer is not properlyadjusted. Such masks or templates may be too large or too small duringprocessing and lead to layers that are larger or smaller than expected.Typically such errors may be in the range of about 1 to 5 nm in size. Tocompensate for magnification errors, a template adjustment device may becoupled to a support configured to hold the template during use. Thetemplate adjustment device may be configured to alter the size of thetemplate during use. By applying forces or altering the temperature ofthe template, the template may be enlarged or contracted. Enlarging orcontracting the template may correct for magnification errors.

[0020] After alignment of the template alignment mark and the substratealignment mark is complete, the processing may be completed. Curinglight may be applied to the light curable liquid. The curing lightcauses the liquid to at least partially cure. After the liquid is atleast partially cured, the template may be removed and the cured liquidwill include structures that are complementary to the pattern etchedonto the template.

[0021] The above-described alignment methods may be used for localalignment processing or global alignment processing. Local alignmentprocessing may be used to process a plurality of semiconductor deviceson a substrate. After forming a patterned layer on a first semiconductordevice, a patterned template may be used to form the same patternedlayer for a second semiconductor device. The substrate may be moved to anew position for processing of the second semiconductor device. In localalignment processing, the template may be realigned with the substratewhen moved to the new portion of the substrate using the alignment markson the template and substrate. In this manner, alignment may be assuredfor each semiconductor device produced.

[0022] Using a separate alignment for each semiconductor device producedon a substrate may be a time intensive process. To minimize processingdelays, global alignment processing may be used. Global alignmentprocessing uses an initial alignment evaluation to allow processing ofadditional devices without further alignment. In one embodiment, analignment of the template with the substrate may be performed at a firstportion of the substrate. After the template is aligned with thesubstrate a patterned layer may be formed using the above-describedimprint lithography process. The positioning of the template withrespect to the substrate in order to achieve the correct alignment maybe herein referred to as the “calibration orientation.” The calibrationorientation may be determined by looking at a single portion of thesubstrate or at multiple portions of the substrate. The calibrationorientation may be determined and recorded. After processing, thetemplate may be moved (commonly referred to as “stepped”) to the nextportion of the substrate to be processed. The movement of the substratewith respect to the template may be very precisely controlled such thatthe change in position of the substrate with respect to the template maybe accurately determined. After movement of the substrate, theorientation of the template with respect to the substrate may bedetermined and compared the calibration orientation. The templateposition may be altered to match the calibration orientation withouthaving to check the alignment of the template with alignment marks. Thismay improve processing speed and overall throughput when using imprintlithography processing.

[0023] The X-Y placement errors induced during the processing ofmultiple portions of a substrate may be measured and compensated usingcapacitance sensors or laser interferometry. The resolution of thesesensors can be sub-nanometer. The sides of template may be either coatedwith a thin layer of conductive metals or reflective materials forimplementing capacitive and interferometric sensing, respectively.

[0024] During the processing of semiconductor devices, a plurality oflayers may be formed to create the device. Each layer is overlaid upon apreviously formed layer during processing. In some embodiments eachlayer formed on the substrate may include an alignment mark. Thealignment mark on the substrate may be formed from a structure disposedon the patterned template that will imprint the alignment mark onto theformed layer. In one embodiment, a template may include a templatealignment mark and an imprinting mark. The alignment mark may be used toalign the template with the substrate by comparing the orientation ofthe substrate alignment mark with the template alignment mark. Theimprinting mark may be used to create a new substrate alignment mark onthe formed layer. The new substrate alignment mark may be used to alignthe template with the substrate during the production of additionallayers.

[0025] An advantage of the above-described embodiments is that bymeasuring and correcting overlay errors while the template and substrateis maintained at an optimal gap, the error correction can be achieved byavoiding stiction and high viscous friction. This optimal gap is highenough to avoid stiction and high viscous friction, while it is lowenough that the induced overlay error during the closing-gap motionbetween the template and substrate can be also minimized.

BRIEF DESCRIPTION OF THE DRAWINGS

[0026] Other objects and advantages of the invention will becomeapparent upon reading the following detailed description and uponreference to the accompanying drawings in which:

[0027]FIGS. 1A and 1B depict a cross-sectional view of the gap between atemplate and a substrate;

[0028] FIGS. 2A-2E depict cross-sectional views of an imprintlithography process;

[0029]FIG. 3 depicts a process flow chart showing the sequence of stepsof the imprint lithography process;

[0030]FIG. 4 depicts a bottom view of a patterned template;

[0031]FIG. 5 depicts a cross-sectional view of a template positionedover a substrate;

[0032]FIG. 6 depicts a cross sectional view of an imprint lithographyprocess using a transfer layer;

[0033]FIG. 7 depicts a cross-sectional view of a process for forming animprint lithography template;

[0034] FIGS. 8A-8C depict a cross-sectional views of patternedtemplates;

[0035]FIG. 9 depicts a cross sectional view of alternate patternedtemplate designs;

[0036] FIGS. 10A-10B depict a top view of a process for applying acurable fluid to a substrate;

[0037]FIG. 11 depicts a schematic of an apparatus for dispensing a fluidduring an imprint lithographic process;

[0038]FIG. 12 depicts fluid dispensing patterns used in an imprintlithographic process;

[0039]FIG. 13 depicts a fluid pattern that includes a plurality of dropson a substrate;

[0040]FIG. 14 depicts a schematic of an alternate apparatus fordispensing a fluid during an imprint lithographic process;

[0041] FIGS. 15A-15B depict a fluid pattern that includes a plurality ofsubstantially parallel lines;

[0042]FIG. 16 depicts a projection view of a substrate support system;

[0043]FIG. 17 depicts a projection view of an alternate substratesupport system;

[0044]FIG. 18 is a schematic diagram of a 4-bar linkage illustratingmotion of the flexure joints;

[0045]FIG. 19 is a schematic diagram of a 4-bar linkage illustratingalternate motion of the flexure joints;

[0046]FIG. 20 is a projection view of a magnetic linear servo motor;

[0047]FIG. 21 is a process flow chart of global processing of multipleimprints;

[0048]FIG. 22 is a process flow chart of local processing of multipleimprints;

[0049]FIG. 23 is a projection view of the axis of rotation of a templatewith respect to a substrate;

[0050]FIG. 24 depicts a measuring device positioned over a patternedtemplate;

[0051]FIG. 25 depicts a schematic of an optical alignment measuringdevice;

[0052]FIG. 26 depicts a scheme for determining the alignment of atemplate with respect to a substrate using alignment marks;

[0053]FIG. 27 depicts a scheme for determining the alignment of atemplate with respect to a substrate using alignment marks usingpolarized filters;

[0054]FIG. 28 depicts a schematic view of a capacitive templatealignment measuring device;

[0055]FIG. 29 depicts a schematic view of a laser interferometeralignment measuring device;

[0056]FIG. 30 depicts a scheme for determining alignment with a gapbetween the template and substrate when the gap is partially filled withfluid;

[0057]FIG. 31 depicts an alignment mark that includes a plurality ofetched lines;

[0058]FIG. 32 depicts a projection view of an orientation stage;

[0059]FIG. 33 depicts an exploded view of the orientation stage;

[0060]FIG. 34 depicts a process flow of a gap measurement technique;

[0061]FIG. 35 depicts a cross sectional view of a technique fordetermining the gap between two materials;

[0062]FIG. 36 depicts a graphical representation for determining localminimum and maximum of a gap;

[0063]FIG. 37 depicts a template with gap measuring recesses;

[0064]FIG. 38 depicts a schematic for using an interferometer to measurea gap between a template and interferometer;

[0065]FIG. 39 depicts a schematic for probing the gap between a templateand a substrate using a probe-prism combination;

[0066]FIG. 40 depicts a cross-sectional view of an imprint lithographicprocess;

[0067]FIG. 41 depicts a schematic of a process for illuminating atemplate;

[0068] FIGS. 42A-B depict a projection view of a flexure member;

[0069]FIG. 43 depicts a first and second flexure member assembled foruse;

[0070]FIG. 44 depicts a projection view of the bottom of an orientationstage;

[0071]FIG. 45 depicts a schematic view of a flexure arm;

[0072]FIG. 46 depicts a cross-sectional view of a pair of flexure arms;

[0073]FIG. 47 depicts a scheme for planarization of a substrate;

[0074] FIGS. 48A-B depicts various views of a vacuum chuck for holding asubstrate;

[0075] FIGS. 49A-C depict a scheme for removing a template from asubstrate after curing;

[0076] FIGS. 50A-C depict a cross-sectional view of a method forremoving a template from a substrate after curing;

[0077] FIGS. 51A-B depict a schematic view of a template support system;and

[0078]FIG. 52 depicts a side view of a gap between a template and asubstrate.

[0079] While the invention is susceptible to various modifications andalternative forms, specific embodiments thereof are shown by way ofexample in the drawing and will herein be described in detail. It shouldbe understood, however, that the drawings and detailed descriptionthereto are not intended to limit the invention to the particular formdisclosed, but on the contrary, the intention is to cover allmodifications, equivalents, and alternatives falling within the spiritand scope of the present invention as defined by the appended claims.

DETAILED DESCRIPTION OF THE INVENTION

[0080] Embodiments presented herein generally relate to systems,devices, and related processes of manufacturing small devices. Morespecifically, embodiments presented herein relate to systems, devices,and related processes of imprint lithography. For example, theseembodiments may have application to imprinting very small features on asubstrate, such as a semiconductor wafer. It should be understood thatthese embodiments may also have application to other tasks, for example,the manufacture of cost-effective Micro-Electro-Mechanical Systems (orMEMS). Embodiments may also have application to the manufacture of otherkinds of devices including, but not limited to: patterned magnetic mediafor data storage, micro-optical devices, biological and chemicaldevices, X-ray optical devices, etc.

[0081] With reference now to the figures, and specifically to FIGS. 1Aand 1B, therein are shown arrangements of a template 12 predisposed withrespect to a substrate 20 upon which desired features are to beimprinted using imprint lithography. Specifically, the template 12 mayinclude a surface 14 that is fabricated to take on the shape of desiredfeatures which, in turn, may be transferred to the substrate 20. In someembodiments, a transfer layer 18 may be placed between the substrate 20and the template 12. Transfer layer 18 may receive the desired featuresfrom the template 12 via imprinted layer 16. As is well known in theart, transfer layer 18 may allow one to obtain high aspect ratiostructures (or features) from low aspect ratio imprinted features.

[0082] For the purpose of imprint lithography, it is important tomaintain the template 12 and substrate 20 as close to each other aspossible and nearly parallel. For example, for features that are about100 nm wide and about 100 nm deep, an average gap of about 200 nm orless with a variation of less than about 50 nm across the imprintingarea of the substrate 20 may be required for the imprint lithographyprocess to be successful. Embodiments presented herein provide a way ofcontrolling the spacing between the template 12 and substrate 20 forsuccessful imprint lithography given such tight and precise gaprequirements.

[0083]FIGS. 1A and 1B illustrate two types of problems that may beencountered in imprint lithography. In FIG. 1A, a wedge shaped imprintedlayer 16 results because the template 12 is closer to the substrate 20at one end of the imprinted layer 16. FIG. 1A illustrates the importanceof maintaining template 12 and substrate 20 substantially parallelduring pattern transfer. FIG. 1B shows the imprinted layer 16 being toothick. Both of these conditions may be highly undesirable. Embodimentspresented herein provide systems, processes and related devices whichmay eliminate the conditions illustrated in FIGS. 1A and 1 B as well asother orientation problems associated with prior art lithographytechniques.

[0084]FIGS. 2A through 2E illustrate an embodiment of an imprintlithography process, denoted generally as 30. In FIG. 2A, template 12may be orientated in spaced relation to the substrate 20 so that a gap31 is formed in the space separating template 12 and substrate 20.Surface 14 of template 12 may be treated with a thin layer 13 thatlowers the template surface energy and assists in separation of template12 from substrate 20. The manner of orientation and devices forcontrolling gap 31 between template 12 and substrate 20 are discussedbelow. Next, gap 31 may be filled with a substance 40 that conforms tothe shape of treated surface 14. Alternately, in an embodiment,substance 40 may be dispensed upon substrate 20 prior to moving template12 into a desired position relative to substrate 20.

[0085] Substance 40 may form an imprinted layer such as imprinted layer16 shown in FIGS. 1A and 1 B. Preferably, substance 40 may be a liquidso that it may fill the space of gap 31 rather easily and quicklywithout the use of high temperatures and the gap can be closed withoutrequiring high pressures. Further details regarding appropriateselections for substance 40 are discussed below.

[0086] A curing agent 32 may be applied to the template 12 causingsubstance 40 to harden and assume the shape of the space defined by gap31. In this way, desired features 44 (FIG. 2D) from the template 12 maybe transferred to the upper surface of the substrate 20. Transfer layer18 may be provided directly on the upper surface of substrate 20.Transfer layer 18 may facilitate the amplification of featurestransferred from the template 12 to generate high aspect ratio features.

[0087] As depicted in FIG. 2D, template 12 may be removed from substrate20 leaving the desired features 44 thereon. The separation of template12 from substrate 20 must be done so that desired features 44 remainsintact without shearing or tearing from the surface of the substrate 20.Embodiments presented herein provide a method and associated system forpeeling and pulling (referred to herein as the “peel-and-pull” method)template 12 from substrate 20 following imprinting so that desiredfeature 44 remain intact.

[0088] Finally, in FIG. 2E, features 44 transferred from template 12 tosubstance 40 may be amplified in vertical size by the action of thetransfer layer 18 as is known in the use of bilayer resist processes.The resulting structure may be further processed to complete themanufacturing process using well-known techniques. FIG. 3 summarizes anembodiment of an imprint lithography process, denoted generally as 50,in flow chart form. Initially, at step 52, course orientation of atemplate and a substrate may be performed so that a rough alignment ofthe template and substrate may be achieved. An advantage of courseorientation at step 52 may be that it may allow pre-calibration in amanufacturing environment, where numerous devices are to bemanufactured, with efficiency and with high production yields. Forexample, where the substrate includes one of many die on a semiconductorwafer, course alignment (step 52) may be performed once on the first dieand applied to all other dies during a single production run. In thisway, production cycle times may be reduced and yields may be increased.

[0089] At step 54, a substance may be dispensed onto the substrate. Thesubstance may be a curable organosilicon solution or other organicliquid that may become a solid when exposed to activating light. Thefact that a liquid is used may eliminate the need for high temperaturesand high pressures associated with prior art lithography techniques.Next, at step 56, the spacing between the template and substrate may becontrolled so that a relatively uniform gap may be created between thetwo layers permitting the precise orientation required for successfulimprinting. Embodiments presented herein provide a device and system forachieving the orientation (both course and fine) required at step 56.

[0090] At step 58, the gap may be closed with fine vertical motion ofthe template with respect to the substrate and the substance. Thesubstance may be cured (step 59) resulting in a hardening of thesubstance into a form having the features of the template. Next, thetemplate may separated from the substrate, step 60, resulting infeatures from the template being imprinted or transferred onto thesubstrate. Finally, the structure may be etched, step 62, using apreliminary etch to remove residual material and a well-known oxygenetching technique to etch the transfer layer.

[0091] In various embodiments, a template may incorporate unpatternedregions i) in a plane with the template surface, ii) recessed in thetemplate, iii) protrude from the template, or iv) a combination of theabove. A template may be manufactured with protrusions, which may berigid. Such protrusions may provide a uniform spacer layer useful forparticle tolerance and optical devices such as gratings, holograms, etc.Alternately, a template may be manufactured with protrusions that arecompressible.

[0092] In general, a template may have a rigid body supporting it viasurface contact from: i) the sides, ii) the back, iii) the front or iv)a combination of the above. The template support may have the advantageof limiting template deformation or distortion under applied pressure.In some embodiments, a template may be coated in some regions with areflective coating. In some such embodiments, the template mayincorporate holes in the reflective coating such that light may passinto or through the template. Such coatings may be useful in locatingthe template for overlay corrections using interferometry. Such coatingsmay also allow curing with a curing agent source that illuminatesthrough the sides of the template rather than the top. This may allowflexibility in the design of a template holder, of gap sensingtechniques, and of overlay mark detection systems, among other things.Exposure of the template may be performed: i) at normal incidences tothe template, ii) at inclined angles to the template, or iii) through aside surface of the template. In some embodiments, a template that isrigid may be used in combination with a flexible substrate.

[0093] The template may be manufactured using optical lithography,electron beam lithography, ion-beam lithography, x-ray lithography,extreme ultraviolet lithography, scanning probe lithography, focused ionbeam milling, interferometric lithography, epitaxial growth, thin filmdeposition, chemical etch, plasma etch, ion milling, reactive ion etchor a combination of the above. The template may be formed on a substratehaving a flat, parabolic, spherical, or other surface topography. Thetemplate may be used with a substrate having a flat, parabolic,spherical, or other surface topography. The substrate may contain apreviously patterned topography and/or a film stack of multiplematerials.

[0094] In an embodiment depicted in FIG. 4, a template may include apatterning region 401, an entrainment channel 402, and an edge 403.Template edge 403 may be utilized for holding the template within atemplate holder. Entrainment channel 402 may be configured to entrainexcess fluid thereby preventing its spread to adjacent patterning areas,as discussed in more detail below. In some embodiments, a patternedregion of a template may be flat. Such embodiments may be useful forplanarizing a substrate.

[0095] In some embodiments, the template may be manufactured with amulti-depth design. That is, various features of the template may be atdifferent depths with relation to the surface of the template. Forexample, entrainment channel 402 may have a depth greater thanpatterning area 401. An advantage of such an embodiment may be thataccuracy in sensing the gap between the template and substrate may beimproved. Very small gaps (e.g., less than about 100 nm) may bedifficult to sense; therefore, adding a step of a known depth to thetemplate may enable more accurate gap sensing. An advantage of adual-depth design may be that such a design may enable using astandardized template holder to hold an imprint template of a given sizewhich may include dies of various sizes. A third advantage of adual-depth design may enable using the peripheral region to hold thetemplate. In such a system, all portions of the template and substrateinterface having functional structures may be exposed to the curingagent. As depicted in FIG. 5, a template 500 with the depth of theperipheral region 501 properly designed may abut adjacent imprints 502,503. Additionally, the peripheral region 501 of imprint template 500 mayremain a safe vertical distance away from imprints 503.

[0096] A dual-depth imprint template, as described above, may befabricated using various methods. In an embodiment depicted in FIG. 6, asingle, thick substrate 601 may be formed with both a high-resolution,shallow-depth die pattern 602, and a low-resolution, large-depthperipheral pattern 603. In an embodiment, as depicted in FIG. 7, a thinsubstrate 702 (e.g., quartz wafer) may be formed having ahigh-resolution, shallow-depth die pattern 701. Die pattern 701 may thenbe cut from substrate 702. Die pattern 701 may then be bonded to athicker substrate 703, which has been sized to fit into an imprinttemplate holder on an imprint machine. This bonding may be preferablyachieved using an adhesive 704 with an index of refraction of the curingagent (e.g., UV light) similar to that of the template material.

[0097] Additional imprint template designs are depicted in FIGS. 8A, 8B,and 8C and generally referenced by numerals 801, 802, and 803,respectively. Each of template designs 801, 802 and 803 may includerecessed regions which may be used for gap measurement and orentrainment of excess fluid.

[0098] In an embodiment, a template may include a mechanism forcontrolling fluid spread that is based on the physical properties of thematerials as well as geometry of the template. The amount of excessfluid which may be tolerated without causing loss of substrate area maylimited by the surface energies of the various materials, the fluiddensity and template geometry. Accordingly, a relief structure may beused to entrain the excess fluid encompassing a region surrounding thedesired molding or patterning area. This region may generally bereferred to as the “kerf.” The relief structure in the kerf may berecessed into the template surface using standard processing techniquesused to construct the pattern or mold relief structure, as discussedabove.

[0099] In conventional photolithography, the use of optical proximitycorrections in the photomasks design is becoming the standard to produceaccurate patterns of the designed dimensions. Similar concepts may beapplied to micro- and nano-molding or imprint lithography. A substantialdifference in imprint lithography processes may be that errors may notbe due to diffraction or optical interference but rather due to physicalproperty changes that may occur during processing. These changes maydetermine the nature or the need for engineered relief corrections inthe geometry of the template. A template in which a pattern reliefstructure is designed to accommodate material changes (such as shrinkageor expansion) during imprinting, similar in concept to optical proximitycorrection used in optical lithography, may eliminate errors due tothese changes in physical properties. By accounting for changes inphysical properties, such as volumetric expansion or contraction, reliefstructure may be adjusted to generate the exact desired replicatedfeature. For example, FIG. 9 depicts an example of an imprint formedwithout accounting for material property changes 901, and an imprintformed accounting for changes in material properties 902. In certainembodiments, a template with features having a substantially rectangularprofile 904, may be subject to deformations due to material shrinkageduring curing. To compensate for such material shrinkage, templatefeatures may be provided with an angled profile 905.

[0100] With respect to imprint lithography processes, the durability ofthe template and its release characteristics may be of concern. Adurable template may be formed of a silicon or silicon dioxidesubstrate. Other suitable materials may include, but are not limited to:silicon germanium carbon, gallium nitride, silicon germanium, sapphire,gallium arsinide, epitaxial silicon, poly-silicon, gate oxide, quartz orcombinations thereof. Templates may also include materials used to formdetectable features, such as alignment markings. For example, detectablefeatures may be formed of SiOx, where x is less than 2. In someembodiments x may be about 1.5. It is believed that this material may beopaque to visible light, but transparent to some activating lightwavelengths.

[0101] It has been found through experimentation that the durability ofthe template may be improved by treating the template to form a thinlayer on the surface of the template. For example, an alkylsilane, afluoroalkylsilane, or a fluoroalkyltrichlorosilane layer may be formedon the surface, in particular tridecafluoro-1,1,2,2-tetrahydrooctyltrichlorosilane (C₅F₁₃C₂H₄SiCl₃) may be used. Such a treatment may forma self-assembled monolayer (SAM) on the surface of the template.

[0102] A surface treatment process may be optimized to yield low surfaceenergy coatings. Such a coating may be used in preparing imprinttemplates for imprint lithography. Treated templates may have desirablerelease characteristics relative to untreated templates. For example,newly-treated templates may posses surface free energies, _(λtreated) ofabout 14 dynes/cm. Untreated template surfaces may posses surface freeenergies, λ_(untreated) about 65 dynes/cm. A treatment proceduredisclosed herein may yield films exhibiting a high level of durability.Durability may be highly desirable since it may lead to a template thatmay withstand numerous imprints in a manufacturing setting.

[0103] A coatings for the template surface may be formed using either aliquid-phase process or a vapor-phase process. In a liquid-phaseprocess, the substrate may be immersed in a solution of precursor andsolvent. In a vapor-phase process, a precursor may be delivered via aninert carrier gas. It may be difficult to obtain a purely anhydroussolvent for use in liquid-phase treatments. Water in the bulk phaseduring treatment may result in clump deposition, which may adverselyaffect the final quality or coverage of the coating. In an embodiment ofa vapor-phase process, the template may be placed in a vacuum chamber,after which the chamber may be cycle-purged to remove excess water. Someadsorbed water may remain on the surface of the template. A small amountof water may be needed to complete a surface reaction which forms thecoating. It is believed that the reaction may be described by theformula:

R—SiCI3+3H2O=>R—Si(OH)3+3HCl

[0104] To facilitate the reaction, the template may be brought to adesired reaction temperature via a temperature-controlled chuck. Theprecursor may then be fed into the reaction chamber for a prescribedtime. Reaction parameters such as template temperature, precursorconcentration, flow geometries, etc. may be tailored to the specificprecursor and template substrate combination.

[0105] As previously mentioned, substance 40 may be a liquid so that itmay fill the space of gap 31. For example, substance 40 may be a lowviscosity liquid monomer solution. A suitable solution may have aviscosity ranging from about 0.01 cps to about 100 cps (measured at 25degrees C.). Low viscosities are especially desirable forhigh-resolution (e.g., sub-100 nm) structures. In particular, in thesub-50 nm regime, the viscosity of the solution should be at or belowabout 25 cps, or more preferably below about 5 cps (measured at 25degrees C.). In an embodiment, a suitable solution may include a mixtureof 50% by weight n-butyl acrylate and 50% SIA 0210.0(3-acryoloxypropyltristrimethylsiloxane)silane. To this solution may beadded a small percentage of a polymerization initiator (e.g., a photoinitiator). For example, a 3% by weight solution of a 1:1 Irg 819 andIrg 184 and 5% of sm 1402.0 may be suitable. The viscosity of thismixture is about 1 cps.

[0106] In an embodiment, an imprint lithography system may includeautomatic fluid dispensing method and system for dispensing fluid on thesurface of a substrate (e.g., a semiconductor wafer). The dispensingmethod may use a modular automated fluid dispenser with one or moreextended dispenser tips. The dispensing method may use an X-Y stage togenerate relative lateral motions between the dispenser tip and thesubstrate. The method may eliminate several problems with imprintlithography using low viscosity fluids. For example, the method mayeliminate air bubble trapping and localized deformation of an imprintingarea. Embodiments may also provide a way of achieving low imprintingpressures while spreading the fluid across the entire gap between theimprinting template and the substrate, without unnecessary wastage ofexcess fluid.

[0107] In an embodiment, a dispensed volume may typically be less thanabout 130 nl (nano-liter) for a 1 inch² imprint area. After dispensing,subsequent processes may involve exposing the template and substrateassembly to a curing agent. Separation of the template from thesubstrate may leave a transferred image on top of the imprinted surface.The transferred image may lie on a thin layer of remaining exposedmaterial. The remaining layer may be referred to as a “base layer.” Thebase layer should be thin and uniform for a manufacturable imprint.

[0108] Imprint processes may involve high pressures and/or hightemperatures applied at the template and substrate interface. However,for the purpose of a manufacturable imprint lithography processincluding high resolution overlay alignment, high pressures andtemperatures should be avoided. Embodiments disclosed herein avoid theneed for high temperature by using low viscosity photo-curable fluids.Further, imprinting pressures may be minimized by reducing squeezingforce required to spread the fluid across the entire imprinting area.Therefore, for the purpose of fluid based imprint lithography, a fluiddispense process should satisfy the following properties:

[0109] 1. No air bubble should be trapped between template andsubstrate;

[0110] 2. Direct contact between the dispenser tip and substrate shouldbe avoided to minimize particle generation;

[0111] 3. Pressure required to fill the gap between template andsubstrate should be minimized;

[0112] 4. Non-uniform fluid buildup and/or pressure gradients should beminimized to reduce non-uniform localized deformation oftemplate-substrate interface; and

[0113] 5. Waste of the dispensed fluid should be minimized.

[0114] In some embodiments, relative motion between a displacement basedfluid dispenser tip and a substrate may be used to form a pattern withsubstantially continuous lines on an imprinting area. Size of the crosssection of the line and the shape of the line may be controlled bybalancing rates of dispensing and relative motion. During the dispensingprocess, dispenser tips may be fixed near (e.g., on the order of tens ofmicrons) the substrate. Two methods of forming a line pattern aredepicted in FIGS. 10A and 10B. The pattern depicted in FIGS. 10A and 10Bis a sinusoidal pattern; however, other patterns are possible. Asdepicted in FIGS. 10A and 10B a continuous line pattern may be drawnusing either a single dispenser tip 1001 or multiple dispenser tips1002.

[0115] Dispensing rate, V_(d), and relative lateral velocity of asubstrate, v_(s), may be related as follows:

V _(d) =V _(d) /t _(d) (dispensing volume/dispensing period),  (1)

V _(s) =L/t _(d) (line length/dispensing period),  (2)

V _(d) =aL (where, ‘a’ is the cross section area of line pattern),  (3)

[0116] Therefore,

V _(d) =av _(s).  (4)

[0117] The width of the initial line pattern may normally depend on thetip size of a dispenser. The tip dispenser may be fixed. In anembodiment, a fluid dispensing controller 1111 (as depicted in FIG. 11)may be used to control the volume of fluid dispensed (V_(d)) and thetime taken to dispense the fluid (t_(d)). If V_(d) and td are fixed,increasing the length of the line leads to lower height of the crosssection of the line pattern. Increasing pattern length may be achievedby increasing the spatial frequency of the periodic patterns. Lowerheight of the pattern may lead to a decrease in the amount of fluid tobe displaced during imprint processes. By using multiple tips connectedto the same dispensing line, line patterns with long lengths may beformed faster as compared to the case of a single dispenser tip. In anembodiment, a displacement based fluid delivery system may include: afluid container 1101, an inlet tube 1102, an inlet valve 1103, an outletvalve 1104, a syringe 1105, a syringe actuator 1106, a dispenser tip1107, an X stage actuator 1109, a Y stage actuator 1110, a dispensercontroller 1111, an XY stage controller 1112, and a main controlcomputer 1113. A suitable displacement based dispenser may be availablefrom the Hamilton Company.

[0118]FIG. 12 illustrates several undesirable fluid patterns ordispensing methods for low viscosity fluids. These dispensing patternsmay lead to one or more problems, including: trapping air bubbles,localized deformations, and waste of fluid. For example, dispensing asingle drop at the center of the imprinting area 1201, or dispensingirregular lines 1205 may lead to localized deformations of the templateand/or substrate. Dispensing several drops 1202, or lines 1206 in acircumferential pattern may lead to trapping of air bubbles. Otherdispensing patterns with nearly closed circumferential patterns 1204 maysimilarly lead to air bubble trapping. Likewise, spraying or randomplacement of droplets 1203 may lead to trapping of air bubbles.Spin-coating a substrate with a low viscosity fluid may cause a“dewetting” problem due to the thin film instability. Dewetting may leadto formation of numerous small drops of fluid on the substrate, insteadof a thin uniform layer of fluid.

[0119] In an embodiment, a fluid dispensing method may dispense multiplesmall drops of liquid that may later be formed into a continuous body asthey expand. FIG. 13 depicts the case of using five drops of liquid.Here, five drops are used only for the purpose of illustration. Other“open” patterns, such as a sinusoidal line, a “W”, or an “X” may beimplemented using this method. As the template-substrate gap decreases,circular drops 1301 may become thinner and wider causing neighboringdrops to merge together 1302. Therefore, even though the initialdispensing may not include a continuous form, the expanding liquid mayexpel air from the gap between the template and substrate. A patterneffective for use in this method should be dispensed in such a way thatas droplets expand, they do not trap any air between the template andsubstrate.

[0120] Small drops of liquid whose volume may be accurately specifiedmay be dispensed using micro-solenoid valves with a pressure-supportingunit. Another type of the liquid dispensing actuator may include apiezo-actuated dispenser. Advantages of a system with a micro-solenoidvalve dispenser as compared to a displacement based fluid dispenser mayinclude faster dispensing time and more accurate volume control. Theseadvantages may be especially desirable for larger size imprints (e.g.,several inches across). An embodiment of a system includingmicro-solenoid valves is depicted in FIG. 14. The system may include:fluid container 1401, an inlet tube 1402, an inlet valve 1403, a pump1404, an outlet valve 1405, a pump controller 1406, a micro-solenoidvalve 1407, a micro-solenoid valve controller 1408, an X-y stage 1409,an X-Y stage controller 1410, and a main computer 1412. A substrate 1411may be placed on X-Y stage 1409. A suitable micro-solenoid valvedispenser system may be available from the Lee Company.

[0121] A dispensing pattern that may be useful for large imprint areas(e.g., greater than several inches²) is depicted in FIG. 15A. In such anembodiment, parallel lines of fluid 1503 may be dispensed. Parallellines of fluid 1503 may be expanded in such a way that air may beexpelled from the gap as template 1501 approaches substrate 1502. Tofacilitate expanding lines 1503 in the desired manner, template 1501 maybe close to the gap in an intentionally wedged configuration (asdepicted in FIG. 15B). That is, the template/substrate gap may be closedalong lines 1503 (e.g., the wedge angle may be parallel to the lines1503).

[0122] An advantage of providing a well-distributed initial fluid layermay be that the orientation error between the template and substrate maybe compensated for. This may be due to the hydraulic dynamics of thethin layer of fluid and compliance of the orientation stage. The lowerportion of the template may contact the dispensed fluid earlier thanother portions of the template. As the gap between the template andsubstrate gets smaller, the imbalance of reaction forces between thelower and higher portions of the template increases. This imbalance offorces may lead to a correcting motion for the template and substrate,e.g., bring them into a substantially parallel relationship.

[0123] Successful imprint lithography may require precise alignment andorientation of the template with respect to the substrate to control thegap in between the template and substrate. Embodiments presented hereinmay provide a system capable of achieving precise alignment and gapcontrol in a production fabrication process. In an embodiment, thesystem may include a high resolution X-Y translation stage. In anembodiment, the system may provide a pre-calibration stage forperforming a preliminary and course alignment operation between thetemplate and substrate surface to bring the relative alignment to withinthe motion range of a fine movement orientation stage. Thispre-calibration stage may be required only when a new template isinstalled into the apparatus (also sometimes known as a stepper). Thepre-calibration stage may consist of a base plate, a flexure component,and a plurality of micrometers or high resolution actuators coupling thebase plate and the flexure component.

[0124]FIG. 16 depicts an embodiment of an X-Y translation stage in anassembled configuration, and generally referenced by numeral 1600. Theoverall footprint may be less than about 20 inches by 20 inches and theheight may be about 6 inches (including a wafer chuck). Such anembodiment may provide X and Y-axis translation ranges of motion ofabout 12 inches.

[0125] A second embodiment of an X-Y translation stage is depicted inFIG. 17, and generally referenced by numeral 1700. To provide a similarrange of motion to that of X-Y stage 1600, stage 1700 may have a footprint of about 29 inches by 29 inches and a height of about 15 inches(including a wafer chuck). Stages 1600 and 1700 differ mainly in thatadditional linkages 1701 are oriented vertically, thereby providingadditional load bearing support for the translation stage.

[0126] Both X-Y stage 1600 and X-Y stage 1700 are flexure based systems.Flexures are widely used in precision machines since they may offerfrictionless, particle-free and low maintenance operation. Flexures mayalso provide extremely high resolution. However, most flexure basedsystems may possess limited ranges of motion (e.g., sub mm range ofmotion). Embodiments disclosed herein may have a range of motion of morethan 12 inches. It is believed that such stages may be cost-effectivefor lithographic applications, particularly in vacuum. Further, forimprint lithography techniques, the presence of imprint forces may giveembodiments presented herein significant advantages.

[0127] In general, an X-Y stage may include two types of components:actuation components and load-carrying components. Lead screw assemblymechanisms have been widely used where the positioning accuracy is not avery significant factor. For high accuracy applications, ball screwassemblies have been used for both the actuating and load-carryingcomponents. Both of these designs may be prone to problems of backlashand stiction. Further, the need for lubrication may make these designsundesirable for use in vacuum or in particle-sensitive applications(e.g., imprint lithography).

[0128] Additionally, some designs may utilize air bearings. Air bearingsmay substantially eliminate problems of stiction and backlash. However,air bearings may provide limited load bearing capacities. Additionally,air bearings may be unsuitable for use in vacuum environments.

[0129]FIG. 18 shows a schematic of portion of a basic linkage 1800. Link1 (1804) and link 3 (1805) may be of the same length. When a moving body1801 moves along the X-axis, all of the joints in linkage 1800 rotate bythe same absolute angle. It should be noted that the motion range may beindependent of the length of link 2 (1803). Due to kinematicconstraints, link 2 (1803) may remain parallel to a line between joint 1(1806) and joint 4 (1807). In linkage 1800, the range of motion, lm, maybe given as: $\begin{matrix}\begin{matrix}{l_{m} = {2\quad {d_{1}\quad\lbrack {{\cos \quad ( {\theta_{o} - {\alpha_{\max}/2}} )} - {\cos \quad ( {\theta_{o} + {\alpha_{\max}/2}} )}} \rbrack}}} \\{{= {4\quad d_{1}\quad \sin \quad ( \theta_{o} )\quad \sin \quad ( {\alpha_{\max}/2} )}},}\end{matrix} & (5)\end{matrix}$

[0130] where, θ_(o) is the angle of joint 1 (1806) when all flexurejoints are in their equilibrium conditions, α_(max) is the maximumrotation range of the flexure pivots, and d₁ is the length of links 1and 3, (1804) and (1805). As shown in Eqn. (5), for given d₁, the motionrange is maximized when θ₀=90 Degree. Therefore, the link length may begiven as:

d ₁ =l _(m)/[4 sin(α_(max)/2)]  (6)

[0131] Therefore, using an α_(max) of 60°, the minimum link length for a12 inch motion range, is 6 inches.

[0132]FIG. 19 depicts an embodiment of a basic linkage similar tolinkage 1800, but with the addition of two cylindrical disks 1902. Akinematic study shows that if joint 2 1904 and joint 3 1905 of FIG. 19rotate in opposite directions by the same angle, the stage may generatea pure translational motion along the X axis. By adding cylindricaldisks 1902 at flexure joints 2 1904 and 3 1905, the resulting rollingcontact may rotate link 1 1908 and link 2 1906 in opposite directions.In an embodiment, no additional joints or bearings may be required sincecylindrical discs 1902 may be coupled to links 1908 and 1906. In orderto prevent discs 1902 from slipping, an appropriate pre-load may beapplied between the two disks. Compared to conventional stages wheredirect driven mechanisms or bearings may be used, the contact surfacehere may be relatively small, and relatively easy to maintain. Note thatalthough disks 1902 are not depicted in relation to X-Y stages 1600, and1700, disks 1902 may be present in some embodiments. Links 1602 and 1601in FIG. 16 may correspond to links 1908 and 1906 of FIG. 19. Thus disks1902 may be present at location 1603 (as well as other locations notvisible in the FIG. 16). Referring to FIG. 17, disks 1902 may be presentat location 1702 (as well as other locations not visible in FIG. 17).

[0133] As the actuation system for either of stages 1600 or 1700, twolinear servo motors (as depicted in FIG. 20 and referenced by numeral2000) may be suitable. One linear servo motor may serve each translationaxis. Suitable linear servo motors may be available from the TrilogySystems Corporation. An advantage of such linear servo motors may be theabsence of frictional contact. Another advantage of such linear servomotors may be the fact that they may readily produces actuation forcesgreater than about 100 pounds. Therefore, actuation components mayprovide only translational motion control in the X and Y directions. Itshould be noted that in some embodiments, the actuator of the lowerstage might need to be more powerful than the actuator of the upperstage. In some embodiments, laser interferometers may provide a feedbacksignal to control X and Y positioning of the X-Y stage. It is believedthat laser interferometry may provide nm level positioning control.

[0134] Placement errors can be compensated using laser interferometersand high resolution X-Y stages (such as X-Y stage 1700, depicted in FIG.17). If the orientation alignments between the template and substrateare independent from X-Y motions, the placement error may need to becompensated only once for an entire substrate wafer (i.e., “globaloverlay”). If orientation alignments between the template and substrateare coupled with X-Y motions and/or excessive local orientationvariations on substrate exist, then X-Y position changes of the templaterelative to the substrate may need to be compensated for (i.e.,field-to-field overlay). Overlay alignment issues are further discussedwith regard the overlay alignment section. FIGS. 21 and 22 provideglobal and field-to-field overlay error compensation algorithms,respectively.

[0135] In an embodiment, orientation of template and substrate may beachieved by a pre-calibration stage (automatically, using actuators ormanual, using micrometers) and a fine orientation stage, which may beactive or passive. Either or both of these stages may include othermechanisms, but flexure-based mechanisms may be preferred in order toavoid particles. The calibration stage may be mounted to a frame, andthe fine orientation stage may be mounted to the pre-calibration stage.Such an embodiment may thereby form a serial mechanical arrangement.

[0136] A fine orientation stage may include one or more passivecompliant members. A “passive compliant member” may generally refer to amember that gets its motion from compliance. That is, motion may beactivated by direct or indirect contact with the liquid. If the fineorientation stage is passive, then it may be designed to have the mostdominant compliance about two orientation axes. The two orientation axesmay be orthogonal and may lie on the template lower surface (asdescribed with referenced to FIG. 43). The two orthogonal torsionalcompliance values may typically be the same for a square template. Thefine orientation stage may be designed such that when the template isnon-parallel with respect to the substrate, as it makes contact with theliquid, the resulting uneven liquid pressure may rapidly correct theorientation error. In an embodiment, the correction may be affected withminimal, or no overshoot. Further, a fine orientation stage as describedabove may hold the substantially parallel orientation between thetemplate and substrate for a sufficiently long period to allow curing ofthe liquid.

[0137] In an embodiment, a fine orientation stage may include one ormore actuators. For example, piezo actuators (as described withreference to FIG. 46) may be suitable. In such an embodiment, theeffective passive compliance of the fine orientation stage coupled withthe pre-calibration stage should still be substantially torsional aboutthe two orientation axes. The geometric and material parameters of allthe structural and active elements together may contribute to thiseffective passive stiffness. For instance, piezo actuators may also becompliant in tension and compression. The geometric and materialparameters may be synthesized to obtain the desired torsional complianceabout the two orthogonal orientation axes. A simple approach to thissynthesis may be to make the compliance of the actuators along theiractuation direction in the fine orientation stage higher than thestructural compliances in the rest of the stage system. This may providepassive self-correction capability when a non-parallel template comesinto contact with the liquid on the substrate. Further, this complianceshould be chosen to allow for rapidly correcting orientation errors,with minimal or no overshoot. The fine orientation stage may hold thesubstantially parallel orientation between the template and substratefor sufficiently long period to allow curing of the liquid.

[0138] Overlay alignment schemes may include measurement of alignmenterrors followed by compensation of these errors to achieve accuratealignment of an imprint template, and a desired imprint location on asubstrate. The measurement techniques used in proximity lithography,x-ray lithography, and photolithography (e.g., laser interferometry,capacitance sensing, automated image processing of overlay marks on themask and substrate, etc) may be adapted for the imprint lithographyprocess with appropriate modifications.

[0139] Types of overlay errors for lithography processes may includeplacement error, theta error, magnification error, and mask distortionerror. An advantage of embodiments disclosed herein may be that maskdistortion errors may not be present because the disclosed processes mayoperate at relatively low temperatures (e.g., room temperature) and lowpressures. Therefore, these embodiments may not induce significantdistortion. Further, these embodiments may use templates that are madeof a relatively thick substrate. This may lead to much smaller mask (ortemplate) distortion errors as compared to other lithography processeswhere masks are made of relatively thin substrates. Further, the entirearea of the templates for imprint lithography processes may betransparent to the curing agent (e.g., UV light), which may minimizeheating due to absorption of energy from the curing agent. The reducedheating may minimize the occurrence of heat-induced distortions comparedto photolithography processes where a significant portion of the bottomsurface of a mask may be opaque due to the presence of a metalliccoating.

[0140] Placement error may generally refer to X-Y positioning errorsbetween a template and substrate (that is, translation along the Xand/or Y-axis). Theta error may generally refer to the relativeorientation error about Z-axis (that is, rotation about the Z-axis).Magnification error may generally refer to thermal or material inducedshrinkage or expansion of the imprinted area as compared to the originalpatterned area on the template.

[0141] In imprint lithography processes, orientation alignment for gapcontrol purposes between a template and substrate corresponding to theangles α and β in FIG. 23 may need to be performed frequently ifexcessive field-to-field surface variations exist on the substrate. Ingeneral, it is desirable for the variation across an imprinting area tobe smaller than about one-half of the imprinted feature height. Iforientation alignments are coupled with the X-Y positioning of thetemplate and substrate, field-to-field placement error compensations maybe necessary. However, embodiments of orientation stages that mayperform orientation alignment without inducing placement errors arepresented herein.

[0142] Photolithography processes that use a focusing lens system mayposition the mask and substrate such that it may be possible to locatethe images of two alignment marks (one on the mask and the other on thesubstrate) onto the same focal plane. Alignment errors may be induced bylooking at the relative positioning of these alignment marks. In imprintlithography processes, the template and substrate maintain a relativelysmall gap (of the order of micro meters or less) during the overlayerror measurement. Therefore, overlay error measurement tools may needto focus two overlay marks from different planes onto the same focalplane. Such a requirement may not be critical for devices with featuresthat are relatively large (e.g., about 0.5 J.lm). However, for criticalfeatures in the sub-100 nm region, the images of the two overlay marksshould to be captured on the same focal plane in order to achieve highresolution overlay error measurements.

[0143] Accordingly, overlay error measurement and error compensationmethods for imprint lithography processes should satisfy the followingrequirements:

[0144] 1. Overlay error measurement tools should be able to focus on twooverlay marks that are not on the same plane;

[0145] 2. Overlay error correction tools should be able to move thetemplate and substrate relatively in X and Y in the presence of a thinlayer of fluid between the template and substrate;

[0146] 3. Overlay error correction tools should be able to compensatefor theta error in the presence of a thin layer of fluid between thetemplate and substrate; and

[0147] 4. Overlay error correction tools should be able to compensatefor magnification error.

[0148] The first requirement presented above can be satisfied by i)moving an optical imaging tool up and down (as in U.S. Pat. No.5,204,739) or ii) using illumination sources with two differentwavelengths. For both these approaches, knowledge of the gap measurementbetween the template and the substrate is useful, especially for thesecond method. The gap between the template and substrate may bemeasured using one of existing non-contact film thickness measurementtools including broad-band interferometry, laser interferometry andcapacitance sensors.

[0149]FIG. 24 illustrates the positions of template 2400, substrate2401, fluid 2403, gap 2405 and overlay error measurement tools 2402. Theheight of a measuring tool may be adjusted 2406 according to the gapinformation to acquire two overlay marks on the same imaging plane. Inorder to fulfill this approach an image storing 2407 device may berequired. Additionally, the positioning devices of the template andwafer should be vibrationally isolated from the up and down motions ofthe measuring device 2402. Further, when scanning motions in X-Ydirections between the template and substrate are needed for highresolution overlay alignment, this approach may not produce continuousimages of the overlay marks. Therefore, this approach may be adapted forrelatively low-resolution overlay alignment schemes for the imprintlithography process.

[0150]FIG. 25 illustrates an apparatus for focusing two alignment marksfrom different planes onto a single focal plane. Apparatus 2500 may usethe change of focal length resulting from light with distinctwavelengths being used as the illumination sources. Apparatus 2500 mayinclude an image storage device 2503, and illumination source (notshown), and a focusing device 2505. Light with distinct wavelengths maybe generated either by using individual light sources or by using asingle broad band light source and inserting optical band-pass filtersbetween the imaging plane and the alignment marks. Depending on the gapbetween the template 2501 and substrate 2502, a different set of twowavelengths may be selected to adjust the focal lengths. Under eachillumination, each overlay mark may produce two images on the imagingplane as depicted in FIG. 26. A first image 2601 may be a clearlyfocused image. A second image 2602 may be an out-of-focus image. Inorder to eliminate each out-of-focus image, several methods may be used.

[0151] In a first method, under illumination with a first wavelength oflight, two images may be received by an imaging array (e.g., a CCDarray). Images which may be received are depicted in FIG. 26 andgenerally referenced by numeral 2604. Image 2602 may correspond to anoverlay alignment mark on the substrate. Image 2601 may correspond to anoverlay alignment mark on the template. When image 2602 is focused,image 2601 may be out-of-focus, and visa-versa. In an embodiment, animage processing technique may be used to erase geometric datacorresponding to pixels associated with image 2602. Thus, the out offocus image of the substrate mark may be eliminated, leaving image 2601.Using the same procedure and a second wavelength of light, image 2605and 2606 may be formed on the imaging array. The procedure may eliminateout of focus image 2606. Thus image 2605 may remain. The two remainingfocused images 2601 and 2605 may then be combined onto a single imagingplane 2603 for making overlay error measurements.

[0152] A second method may utilize two coplanar polarizing arrays, asdepicted in FIG. 27, and polarized illumination sources. FIG. 27illustrates overlay marks 2701 and orthogonally polarized arrays 2702.Polarizing arrays 2702 may be made on the template surface or may beplaced above it. Under two polarized illumination sources, only focusedimages 2703 (each corresponding to a distinct wavelength andpolarization) may appear on the imaging plane. Thus, out of focus imagesmay be filtered out by polarizing arrays 2702. An advantage of thismethod may be that it may not require an image processing technique toeliminate out-of-focused images.

[0153] It should be noted that, if the gap between the template andsubstrate is too small during overlay measurement, error correction maybecome difficult due to stiction or increased shear forces of the thinfluid layer. Additionally, overlay errors may be caused by the non-idealvertical motion between the template and substrate if the gap is toolarge. Therefore, an optimal gap between the template and substrateshould to be determined, where the overlay error measurements andcorrections may be performed.

[0154] Moiré pattern based overlay measurement has been used for opticallithography processes. For imprint lithography processes, where twolayers of Moiré patterns are not on the same plane but still overlappedin the imaging array, acquiring two individual focused images may bedifficult to achieve. However, carefully controlling the gap between thetemplate and substrate within the depth of focus of the opticalmeasurement tool and without direct contact between the template andsubstrate may allow two layers of Moiré patterns to be simultaneouslyacquired with minimal focusing problems. It is believed that otherstandard overlay schemes based on the Moiré patterns may be directlyimplemented to imprint lithography process.

[0155] Placement errors may be compensated for using capacitance sensorsor laser interferometers, and high resolution X-Y stages. In anembodiment where orientation alignments between the template andsubstrate are independent from X-Y motions, placement error may need tobe compensated for only once for an entire substrate (e.g., asemiconductor wafer). Such a method may be referred to as a “globaloverlay.” If orientation alignments between the template and substrateare coupled with X-Y motions and excessive local orientation variationsexist on the substrate, X-Y position change of the template may becompensated for using capacitance sensors and/or laser interferometers.Such a method may be referred to as a “field-to-field overlay.” FIGS. 28and 29 depict suitable sensor implementations. FIG. 28 depicts anembodiment of a capacitance sensing system. A capacitance sensing systemmay include capacitance sensors 2801, a conductive coating 2802, on atemplate 2803. Thus, by sensing differences in capacitance, the locationof template 2803 may be determined. Similarly, FIG. 29 depicts anembodiment of a laser interferometer system including reflective coating2901, laser signal 2902 and receiver 2903. Laser signals received byreceiver 2903 may be used to determine the location of template 2904.

[0156] The magnification error, if any exists, may be compensated for bycarefully controlling the temperature of the substrate and the template.Using the difference of the thermal expansion properties of thesubstrate and template, the size of pre-existing patterned areas on thesubstrate may be adjusted to that of a new template. However, it isbelieved that the magnification error may be much smaller in magnitudethan placement error or theta error when an imprint lithography processis conducted at room temperature and low pressures.

[0157] The theta error may be compensated for using a theta stage thathas been widely used for photolithography processes. Theta error may becompensated for by using two separate alignment marks that are separatedby a sufficiently large distance to provide a high resolution thetaerror estimate. The theta error may be compensated for when the templateis positioned a few microns apart from the substrate. Therefore, noshearing of existing patterns may occur.

[0158] Another concern with overlay alignment for imprint lithographyprocesses that use UV curable liquid materials may be the visibility ofthe alignment marks. For the overlay error measurement, two overlaymarks, one on the template and the other on the substrate may be used.However, since it may be desirable for the template to be transparent toa curing agent, the template overlay marks may typically not includeopaque lines. Rather, the template overlay marks may be topographicalfeatures of the template surface. In some embodiment, the marks may bemade of the same material as the template. In addition, UV curableliquids may tend to have refractive indices that are similar to those ofthe template materials (e.g., quartz). Therefore, when the UV curableliquid fills the gap between the template and the substrate, templateoverlay marks may become very difficult to recognize. If the templateoverlay marks are made with an opaque material (e.g., chromium), the UVcurable liquid below the overlay marks may not be properly exposed tothe UV light, which is highly undesirable.

[0159] Two methods are disclosed to overcome the problem of recognizingtemplate overlay mark in the presence of the liquid. A first method usesan accurate liquid dispensing system along with high-resolution gapcontrolling stages. Suitable liquid dispensing systems and the gapcontrolling stages are disclosed herein. For the purpose ofillustration, three steps of an overlay alignment are depicted in FIG.30. The locations of the overlay marks and the patterns of the fluiddepicted in FIG. 30 are only for the purpose of illustration and shouldnot be construed in a limiting sense. Various other overlay marks,overlay mark locations, and/or liquid dispensing patterns are alsopossible. First, in step 3001, a liquid 3003 may be dispensed ontosubstrate 3002. Then, in step 3004, using the high-resolutionorientation stage, the gap between template 3005 and substrate 3002 maybe carefully controlled so that the dispensed fluid 3003 does not fillthe gap between the template and substrate completely. It is believedthat at step 3004, the gap may be only slightly larger than the finalimprinting gap. Since most of the gap is filled with the fluid, overlaycorrection can be performed as if the gap were completely filled withthe fluid. Upon the completion of the overlay correction, the gap may beclosed to a final imprinting gap (step 3006). This may enable spreadingof the liquid into the remaining imprint area. Since the gap changebetween steps 3004 and 3006 may be very small (e.g., about 10 nm), thegap closing motion is unlikely to cause any significant overlay error.

[0160] A second method may be to make special overlay marks on thetemplate that may be seen by the overlay measurement tool but may not beopaque to the curing agent (e.g., UV light). An embodiment of thisapproach is illustrated in FIG. 31. In FIG. 31, instead of completelyopaque lines, overlay marks 3102 on the template may be formed of finepolarizing lines 3101. For example, suitable fine polarizing lines mayhave a width about ½ to ¼ of the wavelength of activating light used asthe curing agent. The line width of polarizing lines 3101 should besmall enough so that activating light passing between two lines isdiffracted sufficiently to cause curing of all the liquid below thelines. In such an embodiment, the activating light may be polarizedaccording to the polarization of overlay marks 3102. Polarizing theactivating light may provide a relatively uniform exposure to all thetemplate regions including regions having overlay marks 3102. Light usedto locate overlay marks 3102 on the template may be broadband light or aspecific wavelength that may not cure the liquid material. This lightneed not be polarized. Polarized lines 3101 may be substantially opaqueto the measuring light, thus making the overlay marks visible usingestablished overlay error measuring tools. Fine polarized overlay marksmay be fabricated on the template using existing techniques, such aselectron beam lithography.

[0161] In a third embodiment, overlay marks may be formed of a differentmaterial than the template. For example, a material selected to form thetemplate overlay marks may be substantially opaque to visible light, buttransparent to activating light used as the curing agent (e.g., UVlight). For example, SiOx where x is less than 2 may form such amaterial. In particular, it is believed that structures formed of SiOxwhere x is about 1.5 may be substantially opaque to visible light, buttransparent to UV light.

[0162]FIG. 32, depicts an assembly of a system, denoted generally as100, for calibrating and orienting a template, such as template 12,about a substrate to be imprinted, such as substrate 20. System 100 maybe utilized in a machine, such as a stepper, for mass fabrication ofdevices in a production environment using imprint lithography processesas described herein. As shown, system 100 may be mounted to a top frame110 which may provide support for a housing 120. Housing 120 may containthe pre-calibration stage for course alignment of a template 150 about asubstrate (not shown in FIG. 32).

[0163] Housing 120 may be coupled to a middle frame 114 with guideshafts 112 a, 112 b attached to middle frame 114 opposite housing 120.In one embodiment, three (3) guide shafts may be used (the back guideshaft is not visible in FIG. 32) to provide a support for housing 120 asit slides up and down during vertical translation of template 150.Sliders 116 a and 116 b attached to corresponding guide shafts 112 a,112 b about middle frame 114 may facilitate this up and down motion ofhousing 120.

[0164] System 100 may include a disk-shaped base plate 122 attached tothe bottom portion of housing 120. Base plate 122 may be coupled to adisk-shaped flexure ring 124. Flexure ring 124 may support the lowerplaced orientation stage included in first flexure member 126 and secondflexure member 128. The operation and configuration of the flexuremembers 126, 128 are discussed in detail below. As depicted in FIG. 33,the second flexure member 128 may include a template support 130, whichmay hold template 150 in place during the imprinting process. Typically,template 150 may include a piece of quartz with desired featuresimprinted on it. Template 150 may also include other substancesaccording to well-known methods.

[0165] As shown in FIG. 33, actuators 134 a, 134 b and 134 c may befixed within housing 120 and operable coupled to base plate 122 andflexure ring 124. In operation, actuators 134 a, 134 b and 134 c may becontrolled such that motion of the flexure ring 124 is achieved. Motionof the actuators may allow for coarse pre-calibration. In someembodiments, actuators 134 a, 134 b and 134 c may include highresolution actuators. In such embodiments, the actuators may be equallyspaced around housing 120. Such an embodiment may permit very precisetranslation of the ring 124 in the vertical direction to control the gapaccurately. Thus, the system 100 may be capable of achieving coarseorientation alignment and precise gap control of template 150 withrespect to a substrate to be imprinted.

[0166] System 100 may include a mechanism that enables precise controlof template 150 so that precise orientation alignment may be achievedand a uniform gap may be maintained by the template with respect to asubstrate surface. Additionally, system 100 may provide a way ofseparating template 150 from the surface of the substrate followingimprinting without shearing of features from the substrate surface.Precise alignment and gap control may be facilitated by theconfiguration of the first and second flexure members, 126 and 128,respectively.

[0167] In an embodiment, template 5102 may be held in place using aseparated, fixed supporting plate 5101 that is transparent to the curingagent as depicted in FIG. 51. While supporting plate 5101 behindtemplate 5102 may support the imprinting force, applying vacuum betweenfixed supporting plate 5101 and template 5102 may support the separationforce. In order to support template 5102 for lateral forces, piezoactuators 5103 may be used. The lateral supporting forces may becarefully controlled by using piezo actuators 5103. This design may alsoprovide the magnification and distortion correction capability forlayer-to-layer alignment in imprint lithography processes. Distortioncorrection may be very important to overcome stitching and placementerrors present in the template structures made by electron beamlithography, and to compensate for distortion in the previous structurespresent on the substrate. Magnification correction may only require onepiezo actuator on each side of the template (i.e. total of 4 piezoactuators for a four sided template). The actuators may be connected tothe template surface in such a way that a uniform force may be appliedon the entire surface. Distortion correction, on the other hand, mayrequire several independent piezo actuators that may apply independentlycontrolled forces on each side of the template. Depending on the levelof distortion control required, the number of independent piezoactuators may be specified. More piezo actuators may provide bettercontrol of distortion. The magnification and distortion error correctionshould be completed prior to the use of vacuum to constrain the topsurface of the template. This is because magnification and distortioncorrection may be properly controlled only if both the top and bottomsurfaces of the template are unconstrained. In some embodiments, thetemplate holder system of FIG. 51 may have a mechanical design thatcauses obstruction of the curing agent to a portion of the area undertemplate 5102. This may be undesirable because a portion of the liquidbelow template 5102 may not cure. This liquid may stick to the templatecausing problems with further use of the template. This problem with thetemplate holder may be avoided by incorporating a set of mirrors intothe template holder to divert the obstructed curing agent in such a waythat the curing agent directed to the region below one edge of template5102 may be bent to cure an obstructed portion below the other edge oftemplate 5102.

[0168] In an embodiment, high resolution gap sensing may be achieved bydesigning the template such that the minimum gap between the substrateand template falls within a sensing technique's usable range. The gapbeing measured may be manipulated independently of the actual patternedsurface. This may allow gap control to be performed within the usefulrange of the sensing technique. For example, if a spectral reflectivityanalysis technique with a useful sensing range of about 150 nm to 20microns is to be used to analyze the gap, then the template may havefeature patterned into the template with a depth of about 150 nm orgreater. This may ensure that the minimum gap that to be sensed isgreater than 150 nm.

[0169] As the template is lowered toward the substrate, the fluid may beexpelled from the gap between the substrate and the template. The gapbetween the substrate and the template may approach a lower practicallimit when the viscous forces approach equilibrium conditions with theapplied compressive force. This may occur when the surface of thetemplate is in close proximity to the substrate. For example, thisregime may be at a gap height of about 100 nm for a 1 cP fluid when 14kPa is applied for 1 sec to a template with a radius of 1 cm. As aresult, the gap may be self-limiting provided a uniform and parallel gapis maintained. Also, a fairly predictable amount of fluid may beexpelled (or entrained). The volume of fluid entrained may bepredictable based on careful fluid dynamic and surface phenomenacalculations.

[0170] For production-scale imprint patterning, it may be desired tocontrol the inclination and gap of the template with respect to asubstrate. In order to accomplish the orientation and gap control, atemplate manufactured with reticle fabrication techniques may be used incombination with gap sensing technology such as i) single wavelengthinterferometry, ii) multi-wavelength interferometry, iii) ellipsometry,iv) capacitance sensors, or v) pressure sensors.

[0171] In an embodiment, a method of detecting gap between template andsubstrate may be used in computing thickness of films on the substrate.A description of a technique based on Fast Fourier Transform (FFT) ofreflective data obtained from a broad-band spectrometer is disclosedherein. This technique may be used for measuring the gap between thetemplate and the substrate, as well as for measuring film thickness. Formulti-layer films, the technique may provide an average thickness ofeach thin film and its thickness variations. Also, the average gap andorientation information between two surfaces in close proximity, such asthe template-substrate for imprint lithography processes may be acquiredby measuring gaps at a minimum of three distinct points through one ofthe surfaces.

[0172] In an embodiment, a gap measurement process may be based on thecombination of the broad-band interferometry and Fast Fourier Transform(FFT). Several applications in current industry utilized various curvefitting techniques for the broad-band interferometry to measure a singlelayer film thickness. However, it is expected that such techniques maynot provide real time gap measurements, especially in the case ofmulti-layer films, for imprint lithography processes. In order toovercome such problems, first the reflective indexes may be digitized inwavenumber domain, between 1/λ_(high) and 1/λ_(low). Then, the digitizeddata may be processed using a FFT algorithm. This novel approach mayyield a clear peak of the FFT signal that accurately corresponds to themeasured gap. For the case of two layers, the FFT signal may yield twoclear peaks that are linearly related to the thickness of each layer.

[0173] For optical thin films, the oscillations in the reflectivity areperiodic in wavenumber (w) not wavelength (λ), such as shown in thereflectivity of a single optical thin film by the following equation,$R = \frac{\rho_{1,2}^{2} + {\rho_{2,3}^{2}^{{- 2}\quad \alpha \quad d}} - {2\quad \rho_{1,2}\rho_{2,3}^{{- \alpha}\quad d}\quad \cos \quad ( {4\quad \pi \quad n\quad {d/\lambda}} )}}{1 - {( {\rho_{1,2}\rho_{2,3}} )^{2}^{{- 2}\quad \alpha \quad d}} + {2\quad \rho_{1,2}\rho_{2,3}^{{- \alpha}\quad d}\quad \cos \quad ( {4\quad \pi \quad n\quad {d/\lambda}} )}}$

[0174] where ρ_(i,i+1) are the reflectivity coefficients at theinterface of the i−1 and i interface, n is the index of refraction, d isthe thickness to measure of the film (material 2 of FIG. 52), and α isthe absorption coefficient of the film (material 2 of FIG. 52). Here,w=I/λ.

[0175] Due to this characteristic, Fourier analysis may be a usefultechnique to determine the period of the function R represented in termsof w. It is noted that, for a single thin film, a clearly defined singlepeak (P₁) may result when a Fourier transform of R(w) is obtained. Thefilm thickness (d) may be a function of the location of this peak suchas,

d=P ₁/(Δw×2n),  (8)

[0176] where Δw=W_(f)−W_(s); W_(f)=l/λ_(min) and W_(s)=1/λ_(max).

[0177] FFT is an established technique in which the frequency of adiscrete signal may be calculated in a computationally efficient way.Thus, this technique may be useful for in-situ analysis and real-timeapplications. FIG. 34 depicts an embodiment of a process flow of filmthickness or gap, measurement via a FFT process of a reflectivitysignal. For multi-layer films with distinct reflective indexes,locations of peaks in a FFT process may correspond to linearcombinations of each film thickness. For example, a two-layer film maylead to two distinct peak locations in a FFT analysis. FIG. 35 depicts amethod of determining the thickness of two films based on two peaklocations.

[0178] Embodiments presented herein may enable measuring a gap or filmthickness even when the oscillation of the reflectivity data includesless than one full period within the measuring wavenumber range. In sucha case, FFT may result in an inaccurate peak location. In order toovercome such a problem and to extend the lower limit of the measurablefilm thickness, a novel method is disclosed herein. Instead of using aFFT algorithm to compute the period of the oscillation, an algorithm tofind a local minimum (W₁) or maximum point (W₂) of the reflectivitybetween W_(s) and W_(f) may be used to compute the period information:dR/dw=0 at W₁ and W₂. The reflectivity R(w) of Equation 7 has itsmaximum at w=O. Further, the wavenumber range (Δw) of typicalspectrometers may be larger than W_(s). For a spectrometer with 200nm-800 nm wavelength range, Δw=3/800 whereas W_(s)=1/800. Therefore, theoscillation length of the reflectivity data between 0-W_(s) may besmaller than that of Δw. As depicted in FIG. 36, there may be two casesof the locations of minimum and maximum in the Δw range, given that w=0is a maximum point of R(w). Therefore, the film thickness can becomputed as follows:

[0179] Case 1 WWO: a local minimum exists at WI. Therefore, W₁=one halfof the periodic oscillation, and hence d=0.5/(w₁×2n).

[0180] Case 2 WW1: a local maximum exists at W₂. Therefore, W₂=oneperiod of the periodic oscillation, and hence d=1/(w₂×2n)

[0181] A practical configuration of the measurement tool may include abroad-band light source, a spectrometer with fiber optics, a dataacquisition board, and a processing computer. Several existing signalprocessing techniques may improve the sensitivity of the FFT data. Forexample, techniques including but not limited to: filtering,magnification, increased number of data points, different range ofwavelengths, etc., may be utilized with gap or film thicknessmeasurement methods disclosed herein.

[0182] Embodiments disclosed herein include a high precision gap andorientation measurement method between two flats (e.g., a template and asubstrate). Gap and orientation measurement methods presented hereinclude use of broad-band interferometry and fringe basedinterferometry. In an embodiment, a method disclosed herein which usesbroad-band interferometry may overcome a disadvantage of broad-bandinterferometer, namely its inability to accurately measure gaps smallerthan about ¼ of the mean wavelength of the broad-band signal.Interference fringe based interferometry may be used for sensing errorsin the orientation of the template soon after it is installed.

[0183] Imprint lithography processes may be implemented to manufacturesingle and multi-layer devices. Single layer devices, such as micronsize optical mirrors, high resolution light filters and light guides,may be manufactured by forming a thin layer of material in certaingeometric shapes on substrates. The imprinted layer thickness of some ofthese devices may be less than ¼ of the mean wavelength of a broad-bandsignal, and may be uniform across an active area. A disadvantage ofbroad-band interferometer may be that it may be unable to accuratelymeasure gaps smaller than about ¼ of the mean wavelength of thebroad-band signal (e.g., about 180 nm). In an embodiment, micrometersize steps, which may be measured accurately, may be etched into thesurface of the template. As depicted in FIG. 37, steps may be etcheddown in the forms of continuous lines 3701 or multiple isolated dots3702 where measurements may be made. Isolated dots 3702 may bepreferable from the point of view of maximizing the useful active areaon the template. When the patterned template surface is only a fewnanometers from the substrate, a broad-band interferometer may measurethe gap accurately without suffering from minimum gap measurementproblems.

[0184]FIG. 38 depicts a schematic of the gap measurement described here.Probes 3801 may also be used in an inclined configuration, such asdepicted in FIG. 39. If more than three probes are used, the gapmeasurement accuracy may be improved by using the redundant information.For simplicity's sake, the ensuing description assumes the use of threeprobes. The step size, h_(s), is magnified for the purpose ofillustration. The average gap at the patterned area, h_(p), may be givenas:

h _(p)=[(h ₁ +h ₂ +h ₃)/3]−h _(s),  (9)

[0185] When the positions of the probes are known ((X_(i), Y_(i)), whereX and y axes are on the substrate surface), the relative orientation ofthe template with respect to the substrate may be expressed as a unitvector (D) that is normal to the template surface with respect to aframe whose x-y axes lie on the top surface of the substrate.

n=r/∥r∥,  (10)

[0186] where, r=[(X₃, Y₃, h₃)−(X₁, Y₁, h₁)]×[(X₂, Y₂, h₂)−(X₁, Y₁, h₁)].Perfect orientation alignment between two flats may be achieved whenn=(00 I)^(T), or h₁=h₂=h₃.

[0187] Measured gaps and orientations may be used as feedbackinformation to imprinting actuators. The size of the measuringbroad-band interferometric beam may be as small as about 75 μm. For apractical imprint lithography process, it may be desirable to minimizethe clear area used only to measure the gap since no pattern can beetched into at the clear area. Further, blockage of the curing agent dueto the presence of measurement tool should to be minimized.

[0188]FIG. 40 depicts a schematic of multi-layer materials onsubstrates. For example, substrate 4001 has layers 4002, and 4003, andfluid 4005 between substrate 4001 and template 4004. These materiallayers may be used to transfer multiple patterns, one by one vertically,onto the substrate surface. Each thickness may be uniform at the cleararea where a gap measurement may be made using light beams 4006. It hasbeen shown that using broad-band interferometry, the thickness of a toplayer may be measured accurately in the presence of multi-layer films.When the optical properties and thicknesses of lower layer films areknown accurately, the gap and orientation information between thetemplate and substrate surface (or metal deposited surfaces formulti-layer devices) may be obtained by measuring the top layerthickness. The thickness of each layer may be measured using the samesensing measurement probes.

[0189] It may be necessary to perform orientation measurement andcorresponding calibration when a new template is installed or a machinecomponent is reconfigured. The orientation error between the template4102 and substrate 4103 may be measured via an interference fringepattern at the template and substrate interface as depicted in FIG. 41.For two optical flats, the interference fringe pattern may appear asparallel dark and light bands 4101. Orientation calibration may beperformed using a pre-calibration stage as disclosed herein.Differential micrometers may be used to adjust the relative orientationof the template with respect to the substrate surface. Using thisapproach, if no interference fringe band is present, the orientationerror may be corrected to be less than ¼, of the wavelength of lightsource used.

[0190] With reference to FIGS. 42A and 42B, therein are depictedembodiments of the first and second flexure members, 126 and 128,respectively, in more detail. Specifically, the first flexure member 126may include a plurality of flexure joints 160 coupled to correspondingrigid bodies 164, 166. Flexure joints 160 and rigid bodies 164, and 166may form part of arms 172, 174 extending from a frame 170. Flexure frame170 may have an opening 182, which may permit the penetration of acuring agent (e.g., UV light) to reach the template 150 when held insupport 130. In some embodiments, four (4) flexure joints 160 mayprovide motion of the flexure member 126 about a first orientation axis180. Frame 170 of first flexure member 126 may provide a couplingmechanism for joining with second flexure member 128 as illustrated inFIG. 43.

[0191] Likewise, second flexure member 128 may include a pair of arms202, 204 extending from a frame 206. Arms 202 and 204 may includeflexure joints 162 and corresponding rigid bodies 208, 210. Rigid bodies208 and 210 may be adapted to cause motion of flexure member 128 about asecond orientation axis 200. A template support 130 maybe integratedwith frame 206 of the second flexure member 128. Like frame 182, frame206 may have an opening 212 permitting a curing agent to reach template150 which may be held by support 130.

[0192] In operation, first flexure member 126 and second flexure member128 may be joined as shown in FIG. 43 to form orientation stage 250.Braces 220, 222 may be provided in order to facilitate joining of thetwo pieces such that the first orientation axis 180 and secondorientation axis 200 are substantially orthogonal to each other. In sucha configuration, first orientation axis 180 and second orientation mayintersect at a pivot point 252 at approximately the template substrateinterface 254. The fact that first orientation axis 180 and secondorientation axis 200 are orthogonal and lie on interface 254 may providefine alignment and gap control. Specifically, with this arrangement, adecoupling of orientation alignment from layer-to-layer overlayalignment may be achieved. Furthermore, as explained below, the relativeposition of first orientation axis 180 and second orientation axis 200may provide an orientation stage 250 that may be used to separate thetemplate 150 from a substrate without shearing of desired features.Thus, features transferred from the template 150 may remain intact onthe substrate.

[0193] Referring to FIGS. 42A, 42B and 43, flexure joints 160 and 162may be notched shaped to provide motion of rigid bodies 164, 166, 208,210 about pivot axes that are located along the thinnest cross sectionof the notches. This configuration may provide two (2) flexure-basedsub-systems for a fine decoupled orientation stage 250 having decoupledcompliant motion axes 180,200. Flexure members 126, 128 may be assembledvia mating of surfaces such that motion of template 150 may occur aboutpivot point 252 substantially eliminating “swinging” and other motionsthat could shear imprinted features from the substrate. Thus,orientation stage 250 may precisely move the template 150 about a pivotpoint 252; thereby, eliminating shearing of desired features from asubstrate following imprint lithography.

[0194] Referring to FIG. 44, during operation of system 100, aZ-translation stage (not shown) may control the distance betweentemplate 150 and the substrate without providing orientation alignment.A pre-calibration stage 260 may perform a preliminary alignmentoperation between template 150 and the substrate surfaces to bring therelative alignment within the motion range limits of orientation stage250. In certain embodiments, pre-calibration may be required only when anew template is installed into the machine.

[0195] With reference to FIG. 45, therein is depicted a flexure model,denoted generally as 300, useful in understanding the principles ofoperation of a fine decoupled orientation stage, such as orientationstage 250. Flexure model 300 may include four (4) parallel joints:joints 1, 2, 3 and 4, that provide a four-bar-linkage system in itsnominal and rotated configurations. Line 310 may pass though joints 1and 2. Line 312 may pass through joints 3 and 4. Angles <:11 and <:12may be selected so that the compliant alignment (or orientation axis)axis lies substantially on the template-wafer interface 254. For fineorientation changes, rigid body 314 between joints 2 and 3 may rotateabout an axis depicted by Point C. Rigid body 314 may be representativeof rigid bodies 170 and 206 of flexure members 126 and 128.

[0196] Mounting a second flexure component orthogonally onto the firstone (as depicted in FIG. 43) may provide a device with two decoupledorientation axes that are orthogonal to each other and lie on thetemplate-substrate interface 254. The flexure components may be adaptedto have openings to allow a curing agent (e.g., UV light) to passthrough the template 150.

[0197] The orientation stage 250 may be capable of fine alignment andprecise motion of template 150 with respect to a substrate. Ideally, theorientation adjustment may lead to negligible lateral motion at theinterface and negligible twisting motion about the normal to theinterface surface due to selectively constrained high structuralstiffness. Another advantage of flexure members 126, 128 with flexurejoints 160, 162 may be that they may not generate particles asfrictional joints may. This may be an important factor in the success ofan imprint lithography process as particles may be particularly harmfulto such processes.

[0198] Due to the need for fine gap control, embodiments presentedherein may require the availability of a gap sensing method capable ofmeasuring small gaps of the order of 500 nm or less between the templateand substrate. Such a gap sensing method may require a resolution ofabout 50 nanometers, or less. Ideally, such gap sensing may be providedin real-time. Providing gap sensing in real-time may allow the gapsensing to be used to generate a feedback signal to actively control theactuators.

[0199] In an embodiment, a flexure member having active compliance maybe provided. For example, FIG. 46 depicts a flexure member, denotedgenerally as 400, including piezo actuators. Flexure member 400 may becombined with a second flexure member to form an active orientationstage. Flexure member 400 may generate pure tilting motions with nolateral motions at the template-substrate interface. Using such aflexure member, a single overlay alignment step may allow the imprintingof a layer on an entire semiconductor wafer. This is in contrast tooverlay alignment with coupled motions between the orientation andlateral motions. Such overlay alignment steps may lead to disturbancesin X-Y alignment, and therefore may require a complicated field-to-fieldoverlay control loop to ensure proper alignment.

[0200] In an embodiment, flexure member 250 may possess high stiffnessin the directions where side motions or rotations are undesirable andlower stiffness in directions where necessary orientation motions aredesirable. Such an embodiment may provide a selectively compliantdevice. That is, flexure member 250 may support relatively high loadswhile achieving proper orientation kinematics between the template andthe substrate.

[0201] With imprint lithography, it may be desirable to maintain auniform gap between two nearly flat surfaces (i.e., the template and thesubstrate). Template 150 may be made from optical flat glass to ensurethat it is substantially flat on the bottom. The template may bepatterned using electron beam lithography. The substrate (e.g., asemiconductor wafer), however, may exhibit a “potato chip” effectresulting in micron-scale variations on its topography. Vacuum chuck 478(as shown in FIG. 47), may eliminate variations across a surface of thesubstrate that may occur during imprinting.

[0202] Vacuum chuck 478 may serve two primary purposes. First, vacuumchuck 478 may be utilized to hold the substrate in place duringimprinting and to ensure that the substrate stays flat during theimprinting process. Additionally, vacuum chuck 478 may ensure that noparticles are present on the back of the substrate during processing.This may be especially important to imprint lithography, as particlesmay create problems that ruin the device and decrease production yields.FIGS. 48A and 48B illustrate variations of a vacuum chuck suitable forthese purposes according to two embodiments.

[0203] In FIG. 48A, a pin-type vacuum chuck 450 is shown as having alarge number of pins 452. It is believed that vacuum chuck 450 mayeliminate “potato chip” effects as well as other deflections on thesubstrate during processing. A vacuum channel 454 may be provided as ameans of applying vacuum to the substrate to keep it in place. Thespacing between the pins 452 may be maintained such that the substratewill not bow substantially from the force applied through vacuum channel454. At the same time, the tips of pins 452 may be small enough toreduce the chance of particles settling on top of them.

[0204]FIG. 48B depicts a groove-type vacuum chuck 460 with a pluralityof grooves 462 across its surface. Grooves 462 may perform a similarfunction to pins 454 of the pin-type vacuum chuck 450. As shown, grooves462 may take on either a wall shape 464 or a smooth curved cross section466. The cross section of grooves 462 for groove-type vacuum chuck 462may be adjusted through an etching process. Also, the space and size ofeach groove may be as small as hundreds of microns. Vacuum flow to eachof grooves 462 may be provided through fine vacuum channels acrossmultiple grooves that run in parallel with respect to the chuck surface.The fine vacuum channels may be formed along with grooves through anetching process.

[0205]FIG. 47 illustrates the manufacturing process for both pin-typevacuum chuck 450 and groove-type vacuum chuck 460. Using optical flat470, no additional grinding and/or polishing steps may be needed forthis process. Drilling at determined locations on the optical flat 470may produce vacuum flow holes 472. Optical flat 470 may then be maskedand patterned 474 before etching 476 to produce the desired features(e.g., pins or grooves) on the upper surface of the optical flat. Thesurface of optical flat 470 may then be treated 479 using well-knownmethods.

[0206] As discussed above, separation of template 150 from the imprintedlayer may be a critical, final step in the imprint lithography process.Since the template 150 and substrate may be almost perfectly parallel,the assembly of the template, imprinted layer, and substrate leads to asubstantially uniform contact between near optical flats. Such a systemmay usually require a large separation force. In the case of a flexibletemplate or substrate, the separation may be merely a “peeling process.”However, a flexible template or substrate may be undesirable from thepoint of view of high-resolution overlay alignment. In case of quartztemplate and silicon substrate, the peeling process may not beimplemented easily. However, separation of the template from animprinted layer may be performed successfully by a “peel and pull”process. A first peel and pull process is illustrated in FIGS. 49A, 49B,and 49C. A second peel and pull process is illustrated in FIGS. 50A,50B, and 50C. A process to separate the template from the imprintedlayer may include a combination of the first and second peel and pullprocesses.

[0207] For clarity, reference numerals 12, 18, 20, and 40 are used inreferring to the template, transfer layer, substrate, and curablesubstance, respectively, in accordance with FIGS. 1A and 1B. Aftercuring of the substance 40, either the template 12 or substrate 20 maybe tilted to intentionally induce an angle 500 between the template 12and substrate 20. Orientation stage 250 may be used for this purpose.Substrate 20 is held in place by vacuum chuck 478. The relative lateralmotion between the template 12 and substrate 20 may be insignificantduring the tilting motion if the tilting axis is located close to thetemplate-substrate interface. Once angle 500 between template 12 andsubstrate 20 is large enough, template 12 may be separated from thesubstrate 20 using only Z-axis motion (i.e. vertical motion). This peeland pull method may result in desired features 44 being left intact onthe transfer layer 18 and substrate 20 without undesirable shearing.

[0208] A second peel and pull method is illustrated in FIGS. 50A, 50B,50C. In the second peel and pull method, one or more piezo actuators 502may be installed adjacent to the template. The one or more piezoactuators 502 may be used to induce a relative tilt between template 12and substrate 20 (FIG. 50A). An end of piezo actuator 502 may be incontact with substrate 20. Thus, if actuator 502 is enlarged (FIG. 50B),template 12 may be pushed away from substrate 20; thus inducing an anglebetween them. A Z-axis motion between the template 12 and substrate 20(FIG. 50C), may then be used to separate template 12 and substrate 20.An end of actuator 502 may be surface treated similar to the treatmentof the lower surface of template 12 in order to prevent the imprintedlayer from sticking to the surface of the actuator.

[0209] In summary, embodiments presented herein disclose systems,processes and related devices for successful imprint lithography withoutrequiring the use of high temperatures or high pressures. With certainembodiments, precise control of the gap between a template and asubstrate on which desired features from the template are to betransferred may be achieved. Moreover, separation of the template fromthe substrate (and the imprinted layer) may be possible withoutdestruction or shearing of desired features. Embodiments herein alsodisclose a way, in the form of suitable vacuum chucks, of holding asubstrate in place during imprint lithography. Further embodimentsinclude, a high precision X-Y translation stage suitable for use in animprint lithography system. Additionally, methods of forming andtreating a suitable imprint lithography template are provided.

[0210] While this invention has been described with references tovarious illustrative embodiments, the description is not intended to beconstrued in a limiting sense. Various modifications and combinations ofthe illustrative embodiments, as well as other embodiments of theinvention, will be apparent to persons skilled in the art upon referenceto the description. It is, therefore, intended that the appended claimsencompass any such modifications or embodiments.

What is claimed:
 1. An imprint lithography template, said templatecomprising: template alignment marks that are substantially transparentto a first flux of light and that produce an analyzable mark in responseto a second flux of light with said first flux of light differing fromsaid second flux of light.
 2. The template as recited in claim 1,wherein said first flux of light includes ultraviolet light.
 3. Thetemplate as recited in claim 1, wherein said second flux of lightincludes visible light.
 4. The template as recited in claim 1, whereinsaid template alignment marks comprise SiO_(x) with x less than
 2. 5.The template as recited in claim 1, wherein said template alignmentmarks comprise SiO_(x) with x approximately 1.5.
 6. The template asrecited in claim 1, wherein said template is substantially transparentto said first flux of light.
 7. The template as recited in claim 1,wherein said template is substantially transparent to said second fluxof light.
 8. An imprint lithography template, said template comprising:template alignment marks, with said template substantially transparentto a first flux of light and said template alignment marks producing ananalyzable mark in response to a second flux of light with said firstflux of light differing from said second flux of light.
 9. The templateas recited in claim 8, wherein said first flux of light includesultraviolet light.
 10. The template as recited in claim 8, wherein saidsecond flux of light includes visible light.
 11. The template as recitedin claim 8, wherein said template alignment marks comprise SiO_(x) withx less than
 2. 12. The template as recited in claim 8, wherein saidtemplate alignment marks comprise SiO_(x) with x approximately 1.5. 13.The template as recited in claim 8, wherein said template issubstantially transparent to said second flux of light.
 14. The templateas recited in claim 8, wherein said template alignment marks aresubstantially transparent to said first flux of light.
 15. An imprintlithography template, said template comprising: template alignment marksthat are substantially transparent to ultraviolet light and that producean analyzable mark in response to visible light.
 16. The template asrecited in claim 15, wherein said template alignment marks compriseSiO_(x) with x less than
 2. 17. The template as recited in claim 15,wherein said template alignment marks comprise SiO_(x) with xapproximately 1.5.
 18. The template as recited in claim 15, wherein saidtemplate is substantially transparent to said first flux of light. 19.The template as recited in claim 15, wherein said template issubstantially transparent to said second flux of light.